1. Field of the Invention
The present invention relates to a peripheral surface shape measuring apparatus of a roll-like object, and more particularly, relates to a peripheral surface shape measuring apparatus of a roll-like object which measures the peripheral surface shape of a huge roll-like object such as a magnetic tape bulk roll and judges whether or not the peripheral surface of the roll-like object is poorly shaped to have a curve or the like.
2. Description of the Related Art
Magnetic tape is made by cutting a wide magnetic tape bulk roll so that the bulk roll is separated into rolls with the same narrow width. However, in the roll forming of a magnetic tape bulk roll, the winding force at both end parts of the magnetic tape bulk roll is slightly different from that at the central part, and therefore, in some cases, such a bad quality of the peripheral surface shape where the roll peripheral surface has the central part swelling like a curve along the axial direction of the roll is caused. A magnetic tape obtained from a magnetic tape bulk roll with a large degree of this bad quality of the peripheral surface shape does not have a linear shape but has a curved shape. Therefore, the use of such magnetic tape causes the bad quality in electrical output or the like and lowers reliability as a product.
Accordingly, it is necessary that before cutting a magnetic tape bulk roll, the peripheral surface shape of the magnetic tape bulk roll is inspected to examine the degree of the curve, and that one which passes a specific standard is used.
As a conventional peripheral surface shape measuring apparatus of a roll-like object, there is one which is described in Japanese Patent Application Publication No. 8-102064.
As shown in FIGS. 7 and 8, this peripheral surface shape measuring apparatus of a roll-like object is an apparatus which measures the shape of a magnetic tape bulk roll 14, by measuring the displacement amount at the time when a shape sensor a rotates, while moving the contact type shape sensor a which is attached to the concave part of a measuring device and rotates according to the peripheral surface shape of the roll-like object, from one end side of the magnetic tape bulk roll 14 toward the other end side.
However, in the case of the conventional peripheral surface shape measuring apparatus of a roll-like object described in Japanese Patent Application Publication No. 8-102064, the displacement amount at the time when the shape sensor a rotates is measured with respect to the mounting position of the measuring device, and therefore, there is such a disadvantage that the measurement error becomes large unless the measuring device is provided so that the shape sensor a moves completely in parallel to the central axis of the roll-like object 14. For example, if the moving direction of the shape sensor a is inclined to the central axis of the roll-like object 14, the measurement is performed inflating the score by the degree corresponding to the inclination, and the measuring accuracy is lowered. Accordingly, in order to raise the measuring accuracy, the mounting accuracy of the measuring device to the roll-like object 14 should also be raised, but a delicate apparatus is necessary for that purpose, and therefore, not only does the apparatus become complicated but also a cost increase is caused.
The present invention has been achieved in view of the above-described circumstances, and has as its object the provision of an improved peripheral surface shape measuring apparatus of a roll-like object which can simply and accurately measure the peripheral surface shape of a roll-like object.
In order to attain the above described object, the present invention is directed to a peripheral surface shape measuring apparatus of a roll-like object which measures a peripheral surface shape of a roll-like object, comprising: a displacement amount measuring device which has a pinching device that pinches the roll-like object in a diameter direction of the roll-like object with a sensor part and a reference point part arranged opposite to each other, and which measures a displacement amount when the sensor part is relatively displaced in the diameter direction with respect to the reference point part; and a moving device which moves the displacement amount measuring device from one end side of the roll-like object to another end side of the roll-like object in an axial direction of the roll-like object, wherein the peripheral surface shape of the roll-like object is measured on the basis of the displacement amount of the sensor part accompanied by movement of the displacement amount measuring device.
According to the present invention, the peripheral surface shape of the roll-like object is measured by moving the displacement amount measuring device which pinches the roll-like object with the sensor part and the reference point part arranged opposite to each other in the diameter direction of the roll-like object from one end side in the axial direction of the roll-like object to the other end side by using the moving device, and therefore, even if the mounting accuracy of the peripheral surface shape measuring apparatus to the roll-like object is not so high, the peripheral surface shape of the roll-like object can simply and accurately be measured.
Preferably, contact positions to the roll peripheral surface of the sensor part and the reference point part which pinch the roll-like object are within a range of xc2x15 mm with respect to the diameter direction in a plane perpendicular to the diameter direction, and therefore, more accurate measurement is possible.
Preferably, the sensor part and the reference point part are shaped like bars which are perpendicular to an axial direction of the roll-like object and are in parallel to each other, and therefore, even if the contact points of the sensor part and the reference point part slightly deviate from the line in the diameter direction of the roll-like object, the diameter of the roll-like object can surely be measured.
Preferably, a guiding device is further provided to make it easy for the displacement amount measuring device to move in parallel to the central axis of the roll-like object, and therefore, more accurate measurement is possible.